Terahertz time-domain spectroscopy technology(THz-TDS) provides a new method for the identification and study of Chinese herbal medicines. Although the experimental data of electric field intensity indicates that the Chinese herbal samples have no obvious characteristic of spectrum absorption to transmitted terahertz wave, nevertheless, it behaves like a terahertz filter having dependence on the sample’s type and thickness of Chinese herbal medicines. Because it is difficult to prepare a standard thickness of the Chinese herbal medicine sample, a sample thickness normalization scheme which utilizes the data of electric field intensity of the transmitted terahertz wave in the samples with different thicknesses is proposed. Then the electric field intensity data of the transmitted terahertz wave in the standard thickness (1 mm) samples are calculated. And then three parameters(α,β,γ) of each Chinese herbal medicine sample with the standard thickness corresponded low-pass filter are calculated. The experimental results show that the proposed scheme is feasible and can be applied to distinguish the types of Chinese herbal medicines.